Eye health-care practitioners generally divide patient examination into three parts: examination of the cornea, examination of the retina, and a vision function exam including measurement of the refractive status of the eye. The doctor""s findings need to be recorded and the standard method for last century has been to make hand-written notes in the chart. Hand recording of vision function and refractive status is completely satisfactory. Vision function is basically a quantitative assessment by the doctor and six numbers describe the refractive information of both eyes so that the manual recording process is quick and efficient. Recording the clinical status of the cornea and retina is completely different.
For the retinal and corneal eye-health exams what is needed is quantitative clinical data but what has usually been recorded in the past is the doctor""s clinical assessment. For example, an examiner may record, xe2x80x9cthe optical disk has a normal pallorxe2x80x9d which is the clinical perception or, even more simply, the diagnoses, xe2x80x9cthis patient does not have glaucomaxe2x80x9d. Seldom is the actual clinical information recorded, which, in this instance, would be a color image of the optical disk. This lack of documentation leaves open an opportunity for later criticism that the examination or diagnoses was faulty. Further, it is well known in the instance of estimating the pallor, the cup-to-disk ratio, and the like, that making assessments of these quantities are difficult and that the intra-observer variation is large. Especially for these examples, it would be quite beneficial to have a method for making a detailed comparison of changes in the optical disk between exams.
Most retinal exams are accomplished by using the optical aids of the direct ophthalmoscope, binocular indirect ophthalmoscope (BIO) or a special lens with the slit-lamp/biomicroscope.
The direct ophthalmoscope consists of a light and single lens held between the doctor""s and patient""s eye by which the doctor can visualize a very small segment of the retina at a time. The light is considered uncomfortably bright by most patients and skill is required on the part of the clinician. By scanning the visualized area about, a mental image of the posterior pole may be obtained for a basic assessment of retinal health. It is difficult to simply stop the scan and study a given area such as the optical disk because of patient motion and discomfort.
For a more complete visualization of the retina, a BIO may be used. The BIO comprises a lens mounted on a headband in front of each of the doctor""s eyes, a single lens held by hand close to the patient""s eye, and a light also mounted on the doctor""s headband. The field-of-view visualized is wider than that of the direct ophthalmoscope and this instrument is generally used through dilated pupils. With the BIO the doctor can more thoroughly examine the periphery of the retina. Using the BIO requires a great deal of clinical skill and is usually learned over a period of an entire year while the doctor is in training. However, like the direct ophthalmoscope, the doctor must develop a mental picture of the broader features of the eye and, because of the bright light and movements of the patient""s eye, it is difficult to stop and carefully study one portion of the retina.
The slit-lamp is designed for corneal visualization. This instrument is a binocular microscope and a small lamp that projects a narrow rectangle of light into the anterior structures. This microscope, with a special lens and the slit-lamp light, can be used for retinal visualization as well. However, when modified for retinal imaging, its inherent limitations generally prevent it from providing high quality retinal visualizations. The examination can only be done on patients with a dilated iris. The lens is positioned to be very close to the patient""s eye, which in turn makes it very difficult to determine and adjust the alignment for the lens. The contact type lens can be very uncomfortable to the patients. The lens produces strong light reflection from its surfaces, which deteriorate the quality of retinal image greatly. However, with only a slit of light, only small portions of the retina can be observed at a time and patients generally feel that the light intensity if very uncomfortable. Overall, modifications on the slit lamp biomicroscope produce a very substandard retinal visualization system.
Currently, for a through eye exam, and almost always when the BIO is used, it is necessary to dilate the patient""s eye. Dilation comprises the application of eye drops that open the iris to a larger than normal diameter and can not be applied until the refraction portion of the exam is completed. Significant time is required for the drops to take effect. During this time the patient is almost always taking up limited space in the examination room. Further, dilation is very objectionable to patients because of the elapsed time for the dilation to return to normal. Studies show that this alone is a major factor for patients to defer having eye exams. Most patients also find the brightness of the light objectionable and many times to the point of pain. While some BIO""s come equipped with head-mounted cameras, these have not been widely accepted, are regarded as difficult to use, and only image a small portion of the retina at a time in any instance. A hazard of dilation is the risk of inducing acute glaucoma that can lead to immediate blindness. Thus, a system that can accomplish an exam with little or no dilating eye drops and no bright light would be of great advantage.
For accurate documentation sometimes fundus cameras are used as a supplement or replacement for the manual retinal exam. These cameras have been in use since the 1940""s and most of them record images of the retina on film. Film has the disadvantage of requiring processing before an assessment of image quality can be obtained and there is no ability to immediately electronically transfer the image. Some cameras are now being equipped with digital imaging add-on capability. By digital imaging we mean the use of an electronic image sensor such as CCD or CMOS followed by digitization and digital storage means.
In current practice these digital add-ons to existing cameras and are quite bulky and expensive. As a consequence, fundus cameras, digital or film, are usually located in a separate room and a specialized technician is employed to operate them. The high level of acquisition and operating costs for digital cameras has left digital imaging to the domain of high-end clinical sites and they are not used for routine exams. Digital cameras have also been added to slit-lamp biomicroscopes so that they can be used for imaging, but this single purpose application has generally proved to not be cost effective and is seldom implemented.
Although designed for retina imaging, the fundus camera has been used to image the cornea. However, the camera generally produces low quality pictures because the inherent achromatic and spherical optical aberrations when used with an air path and are high and the camera has only a very limit working range. When the cornea is in focus, the patient""s eye is located so close to the camera that it becomes difficult to place a slit-lamp between them and no known commercial product provides a slit-lamp with the fundus camera. If a slit-lamp were added, the lamp would block or distort the view of camera when it is positioned in the front of the objective lens. The built-in internal magnification adjustment for the fundus camera is not adequately designed for the required magnifications of corneal imaging. Thus, as a practical matter, using the fundus camera for corneal imaging is very non-optimal.
In yet another prior art retinal imaging approach, a mechanically driven mirror is used to scan a laser beam about the retina and the reflected intensity is measured to generate an image. These imaging systems, commonly called a scanning laser ophthalmoscope or SLO, usually only provide one laser wavelength and this therefore does not produce a color image, a significant clinical disadvantage. Recently, a system was provided to the market with two laser colors, but even this produces very, very poor color image quality. Even greater limitations are in the relatively long exposure time that allows eye movement during the frame time, the large size, and the high cost.
The laser has been widely used in treatment of various diseases in the anterior and posterior segment of the eye. The BIO or biomicroscope is one method used to deliver the laser to retinal or corneal region. To align the clinician""s eye, the condensing lens and patient""s eye must be in line for viewing, and at same time the laser spot must be directed to the intended area. This is a very challenging task. The slit-lamp biomicroscope, with additional laser delivery attachment and a laser lens (contact or noncontact), is the most commonly used platform. Although it provides a more stable condition for laser procedure, the external attachment makes the system complicated to use. The laser lens is very often being held by one hand of the clinician. Any motion of the lens causes the viewed retinal image to move, especially in the case of high magnification lens. It is not comfortable to hold the laser lens steady during the long laser treatment session which can last for several minutes. The regular illumination to the retina is provided by the slit-lamp in this case. To avoid blocking the laser beam the clinician must maintain certain positions with the slit-lamp while simultaneously projecting the light to the desired area. In addition, the reflected laser light from the laser lens can scatter back in many directions in the room, a result hazardous to others present. Viewing through the biomicroscope and laser lens, the clinician can not simultaneously see the iris and make the judgment on the state of alignment for the lens. As result, there is the risk of accidentally firing the laser on to the iris. The nature of the manual manipulation of the laser beam also makes it difficult to assess the dosage of laser being delivered to the retina if no clear marks are left after the treatment. In a new treatment, photodynamic therapy, the laser power level is below that which would leave a mark on the retina. This, the control of the laser dosage is very critical in PDT treatment. Sometimes, a completely separate system is provided for laser treatment, adding to the expense to well equip an eye doctors office.
What is needed is a relatively low cost, digital, and eye camera for monitoring and recording the conditions of the retinal and corneal regions of the eye. This system would have even greater value if it could be additionally used for laser treatment and retinal stimulus for visual function testing.
The present invention provides a digital camera that combines the functions of the retinal camera and corneal camera into one, single, small, easy to use instrument. The single camera can acquire digital images of a retinal region of an eye, and digital images of a corneal region of the eye. The camera includes a first combination of optical elements for making said retinal digital images, and a second combination of optical elements for making said corneal digital images. In a preferred embodiment, a portion of these elements are shared elements including a first objective element of an objective lens combination, a digital image sensor and at least one eyepiece for viewing either the retina or the cornea. Also, preferably, the retinal combination also includes a first changeable element of said objective lens system for focusing, in combination with said first objective element, portions or all of said retinal region at or approximately at a common image plane. Also, preferably, the retinal combination also includes a retinal illuminating light source, an aperture within said frame and positioned within said first combination to form an effective retinal aperture located at or approximately at the lens of the eye defining an effective retinal aperture position, an infrared camera for determining eye position, and an aperture adjustment mechanism for adjusting the effective retinal aperture based on position signals from said infrared camera. Also, preferably, the cornea combination of elements includes a second changeable element of said objective lens system for focusing, in combination with said first objective element, portions or all of said cornea region at or approximately at a common image plane.
In its retinal mode the camera can obtain images of the retina region with little or no dilating drops. In its cornea mode the camera can obtain corneal images of various magnifications as well. Finally, by looking through the provided binocular eyepieces, all of the classical visualization functions of the slit-lamp biomicroscope are provided as well. Thus, the doctor is enabled, with this one instrument, to perform an entire suite of classical examinations as desired with to image both the anterior and posterior segments of the eye.
The optical system and the electronic imager are compacted to about the size and physical envelope of a slit lamp. Therefore, this system could be mounted at an examination chair in place of a traditional slit lamp and there is no need for an extra room for a retinal imaging system.
The switching between the retina, and cornea modes is done internally, while the optical system is sealed by the front lens. The optical system has two different entrance pupils, one located at the lens of the patient""s eye for operation in retina mode and another near the front objective lens for operation in the cornea mode. The optical design corrects spherical and achromatic aberrations in both configurations. As the result, the proposed system produces high resolution and high contrast images for both the retinal and cornea regions of the eye.
A preferred technique is to take two digital images of anterior or posterior segments of the eye from different entrance pupil positions automatically in less than {fraction (1/10)} of second, then display stereoscopic view immediately and digitally. With proper tools, the stereoscopic images can also be reviewed by clinicians in remote location.
Preferably an infrared sensor that continuously images the cornea and co-axially through the optical system while retinal imaging is being conducted to facilitate alignment to a patient""s eye which may be moving slightly. This reduces the skill level requirements considerably and provides the option to include sophisticated focus sensors. In remote locations where a highly skilled clinician is not available the patient""s eye can be xe2x80x9cdigitally capturedxe2x80x9d and this information sent to a reading center for evaluation.
The system provides a plane in the instrument that is conjugate to the retina and this plane lies on the surface of the electronic image sensor. With certain optical beam splitters, this plane can be made accessible within the instrument at other locations for other uses. The system could be used for testing the performance of the eye as an imaging system. A simple example of this would be to project visual acuity charts or color perception information. A programmable LCD could be used to generate the stimulus.
Besides the regular color images, the proposed system can photograph and display flourescein and indocyanine green angiograms in real time and digitally. The stereo retinal angiograms can also be recorded and viewed by other clinicians.
With this camera the time required for an eye examination is reduced substantially. An image is quickly obtained and with a rather low level of flashed light. Preferably the image is then later examined at leisure and shared with the patient. Images from different dates can be retrieved from the digital storage media. The amount of time spent with the doctor looking about the retina is reduced from several minutes to seconds. The camera is especially useful in diagnosing glaucoma in the early phases because of the ease of detecting changes between eye exams in the status of the eye.
Preferably white LED modules consisting of multiple LEDs will be used as the light sources in both retinal imaging and corneal imaging part of the system. The LED module works either continuously or in pulsed mode. LED modules with different wavelengths will be used as light source for FA and ICG angiograms. A special fiber optical component is used to transform the light output to the shape of ring, resulting in higher light coupling efficiency.
A preferred embodiment provides an internally integrated laser projection system. The laser light can be projected internally from a plane conjugate to the imaging plane to be used for therapeutic purpose. With the help of the infrared alignment system, the alignment is easy and simple. When the system is switched to the retinal imaging mode, the laser beam with the appropriate beam characteristic would be delivered to the retina region. The illumination to the retina is provided internally and independent of the positions of laser beam. When the system is switched to the corneal imaging mode, the laser would be delivered to the corneal region.
With the preferred embodiment functioning in a real-time mode, the operator can observe the retinal/corneal image with aiming laser spot on them, then designate (on the image as presented by the computer) the areas to be treated. The system, under computer control, could apply the laser treatment automatically. Further, tracking systems could be used to further stabilize the image and/or the laser beam location. The location and accumulated energy delivery as a function of location can be determined and monitored, which is important parameter in some therapies.
Because the system alignment, retinal/corneal image and aiming laser spot can be monitored and manipulated by a single joystick in real time remotely, the clinician is free from the restricted posture during the treatment session. The patients can be positioned in a more comfortable position during the procedure. It would greatly reduce the stress imposed on the patients and clinicians.